WET Systems specialize in the development of tailor-made, sustainable solutions to your water quality challenges, with ecologically engineered, nature-based and constructed wetland technologies at the core.

Wetland and Ecological Treatment Systems take advantage of the natural contaminant transformations, energy flows and material balances that occur in wetlands and other aquatic ecosystems, only in a more optimized and engineered way, in order to remove pollutants from water.

By working with Mother Nature (rather than against her), wastewater treatment processes can be engineered to operate with significantly lower use of fossil fuels, chemicals and mechanical equipment compared to conventional technologies. This translates to significant savings in operation and maintenance costs over the life of a system. These benefits often come at the cost of a bigger land area requirement; although through clever design, compact ecological systems are also possible, so it is always worth enquiring before ruling out a more sustainable solution.

With the primary goal of developing the most sustainable, reliable and robust solution for each project, WET Systems actively work with our partners to integrate eco-technologies with other treatment systems (such as activated sludge, MLE, trickling filters, DAF, membranes and mechanical processes). Through careful and sympathetic design, the advantages of various technologies can be harnessed to provide logical and efficient outcomes.

This page provides an overview of the various constructed wetland technologies that WET Systems specialize in.

What are Constructed Wetlands?

A constructed treatment wetland is a water quality improvement system specifically designed to harness and optimise the contaminant degradation and transformation processes that occur in natural wetlands; only in a more engineered and efficient way. They are engineered systems consisting of wetland plants growing in a lined basin. The polluted water to be cleaned flows amongst the stems or roots of the plants and associated soil media or substrate (depending on the specific design).

Most pollutants are transformed into organic matter, inert sediments or harmless gases. The water receives treatment through a range of biogeochemical and physical mechanisms, including microbial degradation, sedimentation, filtration, adsorption, precipitation, oxidation, reduction and uptake by plants, algae and microoganisms growing within the system.

Many of the treatment processes occurring in constructed wetlands are fundamentally fueled by solar energy, via the process of photosynthesis. Plants and algae utilize the energy from the sun to grow, produce biomass and take up water and nutrients. CO2 from the atmosphere is converted into organic matter which subsequently provides food for bacteria and other microorganisms to carry out many of the useful and important pollutant transformation processes. The unique adaptations of wetland plants which enable them to grow and survive in waterlogged conditions also help to transfer oxygen into the root-zone which promotes certain desirable treatment processes, without the need for electromechanical aeration equipment.

Types of Constructed Wetlands

A broad range of different wetland technologies exist, each with their own strengths and weaknesses, suited to different applications. Some are suited to small applications, while others are better for

large-scale projects. Some provide conditions that favour aerobic processes, while others are more suited to anaerobic processes, or a mix of both conditions.

Designing a wastewater treatment system can be thought of in a similar way to building a car. We combine different components depending whether we want the car to go fast or have a lot of pulling power; go off-road or stick to the highway; transport 8 people or carry a 1 tonne load in the back. In a similar way, we select and couple together different types of wetland technologies to build the most appropriate treatment system for the task at hand.

The various constructed wetland designs can be classified into different groups based on the way water flows through the system and the type of vegetation they contain, as described in the article by Fonder and Headley on our Resources page.

An overview of the main types of wetland technology which WET Systems utilise is provided below.

Surface Flow Wetlands (SFWs)

Surface Flow Wetlands, also known as Free-Water Surface (FWS) wetlands, are one of the oldest and most commonly applied types of constructed wetland. They resemble a natural marsh ecosystem, with emergent aquatic vegetation (macrophytes) rooted in a soil substrate. The water is usually shallow (0.1 – 0.6m), flowing predominantly over the surface of the soil, receiving treatment as it flows amongst the stems of the plants and the associated microbial biofilms (periphyton) which grow attached to the submersed plants, leaf litter and soil surfaces.

Compared to other wetland technologies, SFWs are especially suitable for large-scale applications because they can better accommodate high and variable flows and are typically less expensive to build (per unit area).

Common applications:

  • tertiary polishing of sewage effluent
  • urban stormwater
  • agricultural drainage and runoff
  • industrial wastewaters
  • removal of nitrogen, phosphorus, organic matter, suspended solids and hydrocarbons


  • Passive treatment without the need for electricity
  • Relatively minimal hydraulic restrictions make them ideal for large or variable flows
  • Use of topsoil from on-site and minimal need for imported sand and gravel media
  • Provide good habitat and biodiversity values

Subsurface Flow Wetlands

Subsurface Flow (SSF) Wetlands are a group of constructed wetland designs in which the water is passed through a lined basin containing porous media (e.g. sand or gravel), so that the upper surface of the system predominantly remains free of any exposed surface water. These systems are planted with emergent aquatic vegetation and the water passes through the root-zone of the plants. SSF Wetlands can be designed to operate with the water flow in either a horizontal or vertical (up or down) direction, depending on the treatment objectives and process requirements.

Subsurface Flow Wetlands tend to be more expensive to build per unit area than Surface Flow Wetlands due to the use of selected porous media which is typically purchased from off-site. However, in many applications SSF wetlands can provide treatment within a smaller footprint. SSF are highly suitable for small (e.g. household) to medium (e.g. village) sized applications wetlands, but tend to be less appropriate for very large applications due to the challenges in distributing and passing very large flows of water through the sand or gravel substrate.

As implied by the name, Horizontal Subsurface Flow Wetlands (HSSFWs) are designed so that the water passes horizontally from one end of a lined basin to the other end, through a porous media (usually gravel) supporting the growth of emergent wetland plants. These systems are designed so that the gravel bed, typically between 0.5 and 1.0m deep, is continuously submersed to within about 10cm of the upper surface. The water receives treatment as it comes in contact with biofilms growing in the root-zone of the plants and on the surface of the gravel media. Other processes include physical filtration and adsorption.

Some oxygen is transferred into the primarily anoxic substrate via the roots of the wetland plants (a natural adaptation strategy), enabling aerobic and anaerobic treatment processes to occur side-by-side within the one reactor. However, oxygen transfer into the saturated gravel bed is generally slow, making HSSFWs particularly suitable for anoxic or anaerobic treatment processes (e.g. denitrification).

The HSSFW is the work-horse of one of WET Systems most popular residential designs for on-site wastewater management, especially where the owner wants to avoid the use of pumps and electricity:

Common applications:

  • On-site domestic wastewater following a septic tank (secondary treatment)
  • Decentralised systems (villages and remote settlements)
  • Commonly used as a second stage after Vertical Flow Wetlands
  • removal of organic matter, suspended solids, total nitrogen, nitrate


  • No surface water (protects public health and prevents mosquitoes and odours)
  • Passive treatment without the need for electricity
  • Minimal head-loss through the system (good for flat sites)
  • Very robust performance if properly designed and built
  • Very low maintenance
  • A simple solution for removing up to 50% of Total Nitrogen in on-site systems

Vertical Flow Wetlands (VFWs) are a type of Subsurface Flow Wetland designed so that the water passes vertically through the bed of porous media (usually sand or fine gravel) in which emergent wetland plants are growing. In the most common VFW design, the water is intermittently distributed across the upper surface of an unsaturated bed of coarse sand in “pulse” or “batch” loads. The water percolates down through the well oxygenated, unsaturated media and receives treatment as it passes through the root-zone of the plants and contacts attached-growth biofilms growing on the surface of the sand.

Vertical Flow Wetlands with an intermittent downward flow are designed to enhance oxygen transfer into the subsurface environment and provide very good conditions for aerobic treatment processes, along with physical filtration and adsorption by the sand media.

Common applications:

  • On-site domestic wastewater following a septic tank (secondary treatment)
  • Decentralised systems (villages and remote settlements)
  • Wastewaters with high organic load
  • Landfill leachate
  • Often used as a first stage before Horizontal Subsurface Flow Wetlands in “hybrid” designs
  • Recirculating VFW for Total Nitrogen removal (recirculation of the nitrified effluent from the VFW back to the influent to achieve denitrification)
  • removal of organic matter, suspended solids, ammonium (nitrification), total nitrogen


  • Efficient aerobic treatment processes
  • Compact footprint
  • No surface water (protects public health and prevents mosquitoes and odours)
  • On sloping sites, can be designed to use a passive dosing siphon, rather than a pump, for loading the system
  • Can be designed as a Recirculating VFW to achieve very high levels of Total Nitrogen removal from domestic wastewater in a compact system

An intermittent Sand Filter is very similar in design and function to a Vertical Flow Wetland with downward flow through an unsaturated sand bed, except that they are unplanted. The absence of plants in a Sand Filter means that they can be installed as an underground, buried unit which can be desirable in some cases.

Recirculation of a portion of the effluent back to the front end can be integrated into a Vertical Flow Wetland or Sand Filter in order to enhance certain treatment processes (e.g. Total N removal), harmonize variability in influent quality and/or quantity, or dilute the concentration of potentially

inhibitory substances in the inflow (e.g. high levels of ammonia in landfill leachate).Depending on the specific treatment needs, between 50% and 90% of the VFW outflow is typically recirculated back to the inlet. The recirculated portion of effluent is usually mixed with the incoming wastewater in a recirculation tank which may also be designed to provide primary settling and sufficient contact time for anoxic treatment processes to occur, such as denitrification.

One of WET Systems’ most popular on-site and decentralized domestic wastewater management systems integrates a Recirculating VFW, as shown below. This system provides very robust performance and achieves high levels of nitrogen removal, making it suitable for a range of applications; especially in sensitive environments.

WET Systems utilizes a specially adapted design variant of the Vertical Flow Wetland for treatment of raw sewage, septage and sludges. Conceived in Germany by constructed wetland pioneers in the 1950s and 1960s, and subsequently developed, optimised and adopted in France and now widely applied internationally, the Raw Sewage VFW (often referred to as the “French System”) is a true example of an ecologically engineered system, reliant on the service of wetland plants to sustainably treat the wastewater.

Following coarse screening, raw sewage is applied directly to one of three 1st Stage VFW beds; the other 2 beds being in a phase of resting. The organic solids are captured on the top surface of the VFW, while the filtered effluent passes through the sand media receiving further treatment via physical filtering and bio-chemical processes. The effluent leaving the 1st stage VFW has significantly reduced concentrations of solids (TSS), organic matter (BOD) and ammonium (NH4-N), before typically flowing to a 2nd stage consisting of VFWs or HSSFWs for further polishing.

Operating the 1st Stage VFWs with an alternating resting and loading cycle (e.g. 1 week loading, 2 weeks resting) ensures that the accumulating organic residue layer on top and indeed the conditions inside the subsurface filter media remain aerobic. This promotes efficient bio-degradation of the organics and allows nitrification to take place. The resting period also allows the organic residues to dewater, leading to mineralisation and increase in the dry solids content.

Raw Sewage VFWs eliminate the need for anaerobic primary treatment and settling tanks which are the source of odours in most sewage treatment plants. By applying the raw sewage directly onto the aerobic surface of the VFW and keeping the residence time in the sewer network short, the wastewater is never allowed the opportunity to become anaerobic and start smelling; very clever!

Common Applications:

  • Domestic sewage treatment
  • decentralised applications with centralized operational control
  • remote settlements where handling of sludge from conventional systems is problematic


  • Years of scientific study and design optimization in France has made this a relatively space efficient constructed wetland option
  • Avoids the generation of odours and sludge by eliminating anaerobic primary treatment devices
  • Provides good quality secondary treatment for rural and remote communities and decentralized systems
  • Can operate without the use of electricity, utilizing gravity flow and dosing siphons
  • A proven technology with a long case history of thousands of decentralized systems operating for decades throughout France, Germany and the Middle East.

A Saturated Vertical Flow Wetland is designed so that some water is retained within the lined basin so that at least part of the bed of porous media (gravel) remains saturated with water. These systems are designed to operate with either upflow or downflow, depending on the specific application and process requirements. The treatment processes and functions of a Saturated Vertical Flow Wetland are very similar to those of a Horizontal SSF Wetland. However, Saturated VFWs are more appropriate for larger scale applications because they do not suffer the same hydraulic constraints as HSSFWs; much lower flow velocities can be maintained through a Saturated VFW compared to a HSSF Wetland.

Since being pioneered 2 decades ago in North America by the Wetland Engineer, Scott Wallace, Aerated Subsurface Flow Wetlands have become an increasingly popular variant of the Subsurface

Flow Wetland design. Simple, energy efficient, low-pressure aeration lines are included across the bottom of the gravel bed. A steady stream of air bubbles is fed into the bottom of the bed through this network of aeration lines. This active aeration overcomes oxygen transfer limitations and enables greater design and operational control over the treatment process. Thus, oxygen-requiring treatment processes can be achieved in a smaller footprint than other constructed wetland designs.

Aerated SSF Wetlands can be designed with either horizontal or vertical flow, depending mainly on the scale of application and the specific treatment process requirements.

Common applications:

  • On-site domestic wastewater following a septic tank (secondary treatment)
  • Decentralised systems (villages and remote settlements)
  • Wastewaters with a high load of organics and/or ammonium
  • Landfill leachate
  • Industrial wastewaters and hydrocarbon contaminated waters
  • Arid regions in order to minimize the loss of water to evapotranspiration
  • removal of organic matter, suspended solids, ammonium (nitrification), total nitrogen (partial) and pathogens


  • Efficient aerobic treatment processes
  • Very compact footprint
  • No surface water (protects public health and prevents mosquitoes and odours)
  • Simple to operate and maintain, with low operating costs compared to other wastewater treatment systems (e.g. activated sludge)

Sludge & Septage Treatment Wetlands

Sludge Treatment Wetlands (STWs), also known as Sludge Treatment Reed Beds (STRBs), are a specially adapted VFW variant. STWs take advantage of the high evapotranspiration rates and root-zone microbial activity of emergent wetland plants, to dewater and mineralize waste sludge from sewage treatment, septage and potable water treatment. They convert sludge into a high quality, stabilized biosolid product through energy efficient natural processes.

Several basins (typically 6 to 12) are used in parallel, with one bed being loaded (usually for 1 week at a time) while the remaining beds are rested (3 – 6 week rest period under Australian conditions). Sludge loading occurs for approximately 10 years before the stabilised, dewatered biosolids is removed (one basin per year) and land applied as a soil amendment.

Many large systems have been in operation for several decades since the emergence of the technology in Denmark during the 1980’s. This tried and proven, sustainable sludge management technology is now being introduced to Australasia, where the warmer climate conditions leads to enhanced performance and improved efficiency.

Common Applications:

  • Waste (or Surplus) Activated Sludge
  • Septage and other sludges
  • Decentralised and municipal scale systems


  • Decades of scientific study and design optimization in Europe (especially Denmark)
  • Odours are avoided by maintaining aerobic conditions through the operational cycle of resting & loading
  • Converts sludge into a stabilized, high quality biosolids resource with high dry matter content through the action of wetland plants and natural microorganisms
  • Produces a filtrate low in organics and ammonia, reducing the oxygen demand when returned to the sewage treatment works
  • Energy efficient
  • No use of chemicals or mechanical equipment
  • Reduces the carbon footprint of sewage management facilities
  • A proven technology with a long case history of hundreds of large-scale systems operating for decades throughout Denmark, Germany, Sweden, France and elsewhere in Europe

Why Choose WET Systems?


We are an Australian business working throughout Australasia and further afield. Where possible, we support other local businesses and provide volunteer services to local groups in order to build a strong community.


WET Systems has over 20 years of experience in the design and construction of constructed wetlands. We have worked across all states in Australia as well as the Middle East and Europe. We provide Australia’s most experienced constructed wetland design service coupled with excellent standards and honesty.


We work closely with our clients to create, design and implement treatment systems to meet their specific needs. We greatly value client input through all stages of the project and aim to grow strong, trusting relationships in order to create the best outcome.

Contact WET Systems

Contact the wetland & ecological treatment system professionals to learn how we implement ecological-oriented waste water management solutions.